Fixed calc() recursive pattern: it was trying to match against the whole pattern, instead of the second group of brackets. Also simplified the rest of the pattern. (Class-CSS.php)

Not that it matters, but the reason I didn't notice the bug earlier was that usually, calc() calls don't include nested brackets, so I didn't test against a stronger string like 'calc(100% + (7px / 1em))', and even then, it probably would have worked in your browser even if not matched.